1. Field of the Invention
This invention relates to a method of measuring a characteristic of a capacitive type of sensor, a sensor characteristic measuring apparatus, a capacitive type of sensor apparatus, and an IC chip for measuring a sensor characteristic.
2. Description of the Prior Art
In the capacitive type of sensor having a fixed electrode and a movable electrode facing each other, the distance between the fixed electrode and the movable electrode may vary with passage of time. If the distance varies, the characteristic of the sensor varies also. Moreover, the sensor may become breakdown. Thus, it was desired to provide a technique for checking whether the capacitive type of sensor has a desired characteristic.
Japanese patent application provisional publication No. 6-160429 discloses a technique for judging whether the movable electrode contacts with the fixed electrode when a predetermined voltage is applied therebetween. Application of the predetermined voltage therebetween generates an electrostatic attracting force, so that the distance between the fixed and movable electrodes decreases. If the sensor does not have the desired characteristic, the movable electrode may contact with the fixed electrode before application of the predetermined voltage or may not contact with the fixed electrode when the predetermined voltage is applied. This provides judgment whether the sensor has a desired characteristic.
In this diagnostic operation, the movable electrode is subjected to deformation that is considerably larger than deformation during measurement of a physical quantity, so that the sensor may receive unrestorable deformation, and the life of the sensor may be shortened.
Accordingly, it is required to provide a diagnostic of the capacitive type of sensor without damage.
The aim of the present invention is to provide a superior method of measuring a characteristic of a capacitive type of sensor.
The aim of the present invention is to provide a superior sensor characteristic measuring apparatus.
The aim of the present invention is to provide a superior capacitive type of sensor apparatus.
The aim of the present invention is to provide a superior integrated chip for measuring a sensor characteristic.
According to the present invention, a first aspect of the present invention provides a method of measuring a characteristic of a capacitive type of sensor having a capacitor including a movable electrode and a fixed electrode facing each other comprising the steps of:
(a) applying a first predetermined voltage between said movable and fixed electrodes;
(b) measuring a first capacitance between said movable and fixed electrodes in condition of step (a);
(c) applying a second predetermined voltage between said movable and fixed electrodes;
(d) measuring a second capacitance of said capacitor in condition of step (c);
(e) effecting comparison between said first and second electrostatic capacitances; and
(f) obtaining a characteristic of said sensor from a result of step (e).
According to the present invention, a second aspect of the present invention provides a sensor characteristic measuring apparatus for measuring a characteristic of a capacitive type of a sensor having a movable electrode and a fixed electrode facing each other comprising:
applying means for applying first and second predetermined voltages between said movable and fixed electrodes;
measuring means for measuring first and second capacitances between said movable and fixed electrodes when said applying means applies said first and second predetermined voltages between said movable and fixed electrodes, respectively;
comparing means for effecting comparison between said first and second electrostatic capacitances to obtain said characteristic.
According to the present invention, a third aspect of the present invention provides a sensor characteristic measuring apparatus based on the second aspect, wherein said measuring means comprises first and second voltage signal generation means for generating first and second voltage signals of which magnitudes are determined in accordance with said first and second capacitances, respectively and equalizing means for effecting equalization between said first voltage signal outputted when said first predetermined voltage is applied between said movable and fixed electrodes in a predetermined normal condition of said movable and fixed electrodes and said second voltage signal outputted when said second predetermined voltage is applied between said movable and fixed electrodes in said predetermined normal conditions of said movable and fixed electrodes.
According to the present invention, a fourth aspect of the present invention provides a capacitive type of sensor apparatus having a capacitive type of sensor including a capacitor having a movable electrode and a fixed electrode facing each other for measuring a physical quantity and measuring a characteristic of a capacitor comprising:
applying means for applying first and second predetermined voltages between said movable and fixed electrodes;
measuring means for measuring first and second capacitances between said movable and fixed electrodes when said applying means applies said first and second predetermined voltages between said movable and fixed electrodes, respectively; and
comparing means for effecting comparison between said first and second electrostatic capacitances to obtain said characteristic.
According to the present invention, a fifth aspect of the present invention provides a capacitive type of sensor based on the fourth aspect, wherein said measuring means comprises first and second voltage signal generation means for generating first and second voltage signals of which magnitudes are determined in accordance with said first and second capacitances, respectively and equalizing means for effecting equalization between said first voltage signal outputted when said first predetermined voltage is applied between said movable and fixed electrodes in a predetermined normal condition of said movable and fixed electrodes and said second voltage signal outputted when said second predetermined voltage is applied between said movable and fixed electrodes in said predetermined normal conditions of said movable and fixed electrodes.
According to the present invention, a sixth aspect of the present invention provides an integrated circuit chip for measuring a characteristic of a capacitive type of a sensor having a movable electrode and a fixed electrode facing each other comprising:
applying means for applying first and second predetermined voltages between said movable and fixed electrodes;
measuring means for measuring first and second capacitances between said movable and fixed electrodes when said applying means applies said first and second predetermined voltages between said movable and fixed electrodes, respectively; and
comparing means for effecting comparison between said first and second electrostatic capacitances to obtain said characteristic.
According to the present invention, a seventh aspect of the present invention provides an integrated circuit chip based on the sixth aspect, wherein said measuring means comprises first and second voltage signal generation means for generating first and second voltage signals of which magnitudes are determined in accordance with said first and second capacitances, respectively and equalizing means for effecting equalization between said first voltage signal outputted when said first predetermined voltage is applied between said movable and fixed electrodes in a predetermined normal condition of said movable and fixed electrodes and said second voltage signal outputted when said second predetermined voltage is applied between said movable and fixed electrodes in said predetermined normal conditions of said movable and fixed electrodes.